Showing posts with label The Earth and the Universe. Show all posts
Showing posts with label The Earth and the Universe. Show all posts

Monday, June 3, 2013

Latitude

Latitude is the angular distance of a point on the earth's surface, measured in degrees from the centre of the earth. It is parallel to a line, the equator, which lies midway between the poles. These lines are therefore called parallels of latitude, and on a globe are actually circles becoming

Longitude

Imaginary lines running north/south at right angles to the parallels and passing through the poles are known as lines of longitude or meridians. The line of longitude passing through Greenwich (London) is 0 degrees or the prime meridian (so called because all lines of longitude are numbered east or west from it). The longitude of a place is its angular distance east or west of the Greenwich meridian, measured at the centre of the earth. There are 180 degrees of west longitude and similarly 180 degrees of east longitude. However, since there are 360 degrees in a circle. 180 degrees East and 180 degrees West must be one and the same line. Since the earth is spherical and has a circumference calculated at 40,232.5 km, in linear distance each of the 360 degrees of longitude is 40,232.5/360 or 111.757 km. As the parallels of latitude become shorter polewards, so the meridians of longitude, which coverage at the poles, enclose a narrower space. The degree of longitude therefore decreases in length. It is longest at the equator where it measures 111.318 km. At 25 degrees it is 100.95 km; at 45 degrees it is 78.856 km; at 75 degrees, 28.967 km; and at the poles 0 km. There is so much difference in the length of degrees of longitude outside the tropics, that they are not used for calculating distances as in the case of latitude. But they have one very important function, they determine local time in relation to G.M.T. or Greenwich Mean Time, which is sometimes referred to as World Time.
THE POSITION OF A PLACE
It is necessary to be precise in stating the position of a place in degrees, since there are two latitudes X degrees (X degrees North and X degrees South). Similarly, longitude Y degrees refers to either opposite meridians unless we state it as Y degrees east and Y degrees west.

Standard Time and Time Zones

If each town were to keep the time of its own meridian, there would be much difference in local time between one town and the other. At 10.00 a.m. in Kota Bharu (a difference of 2 and half degrees in longitude). In larger countries such as canada, U.S.A., China and U.S.S.R. the confusion arising from time differences alone would drive people mad. Travellers going from one end of the country to the other would have to keep changing their watches if they wanted to keep their appointments. This is impracticable and very inconvenient.
To avoid all these difficulties, a system of standard time is observed by all countries. Most countries adopt their standard time from the central meridian of their countries. The Nigerian government has accepted the meridian of 15 degrees east for the standard time which is one hour ahead of Greenwich Mean Time. The whole world has in fact been divided into 24 Standard Time Zones, each of which differs from the next by 15 degrees in longitude or one hour in time. Most countries adhere to this division but due to the perculiar shapes and locations of some countries, reasonable deviations from the Standard Time Zones cannot be avoided.
Larger countries like U.S.A., Canada and U.S.S.R., which have a great east-west stretch, have to adopt several time zones for practical purposes. U.S.S.R., which extends through almost 165 degrees of longitude, is divided into eleven time zones. When it is 10.00 p.m. on Monday night in Leningrad, it will be almost 7.00 a.m. the following Tuesday morning in Vladivostock. Travellers along the Trans-Siberian Railway have to adjust their watches almost a dozen times before they reach their destination. Both Canada and U.S.A. have five time zones - the Atlantic, Eastern, Central, Mountain and Pacific Time Zones. The difference between the local time of the Atlantic anad Pacific coasts is nearly five hours.

The International Date Line

A traveller going eastwards gains time from Greenwich until he reaches the meridian 180 degrees east when he will be 12 hours ahead of G.M.T. Similarly in going westwards, he loses 12 hours when he reaches 180 degrees west. There is thus a total difference of 24 hours or a whole day between the two sides of the 180 degrees meridian. This is the International Date Line where the date changes by exactly one day when it is crossed. A traveller crossing the date line from east to west loses a whole day (because of the loss in time he has made); and while crossing the date line from west to east he gains a day (because of the gain in time he encountered). Thus when it is midnight, Friday on the Asiatic side, by crossing the line eastwards, he gains a day; it will be midnight Thursday on the American side, i.e. he experiences the same calender date twice! When Magellan's ship eventually arrived home in Spain in 1522 after circumnavigating the world from the Atlantic Ocean to the Pacific Ocean and westwards across the International Date Line, the crew knew nothing about adding a day for the one they had missed. They thought they had arrived on the 5 September. They were shocked to be told that the date was 6 September. A modern aircraft leaving Wellington at 5.00 p.m. on Friday reaches Hawaii, 6601 km away, at 2.00 p.m. the same Friday. The same aircraft on its return journey from Hawaii at 11.00 a.m. on Sunday. Can you explain this?
The International Date Line in the mid-Pacific curves from the normal 180 degrees meridian at the Bering Strait, Tonga and other islands to prevent confusion of day and date in some of the island groups that are cut through by the meridian. Some of them keep Asiatic or New Zealand standard time, others follow the American date and time. To find local time in two places on opposite sides of the International Date Line remember that crossing the 'line' going eastwards a whole day is gained. Crossing the 'line' going westwards a whole day is lost.
Example. If someone in Tokyo (time zone 135 degrees east) telephones a friend in Vancouver on 4 December at 10.00 a.m. what time will his friend receive the call in Vancouver (time zone 120 degrees west)?
1. Longitude difference 180' - 135'E = 45'; 180' - 120'W = 60'; 45' + 60' = 105'
2. Therefore time difference = 105/15 = 7 hours.
3. Vancouver is east of Tokyo, therefore time goes on 7 hours.
4. Going eastwards across I.D.L. a whole day is gained. Therefore the time in Vancouver is 5.00 p.m. on 3 December.

Great Circle Routes

Since the earth is spherical in shape, the shortest distance between any two points on the globe lies along its circumference. There are an infinite number of great circles of equal length running around the globe, e.g. the circle formed by the Greenwich Meridian and the 180 degrees meridian; the circle formed by the 130 degrees west and 50 degrees east meridians. Of the lines of latitude, only the equator is a great circle.
When drawn on a globe great circles appear as straight lines, but when they are drawn on flat maps of the world they may not appear so. In fact on many maps great circles appear curved and routes along a straight line joining two places. This is an illusion created by the distortion of the shape of the earth to allow it to be drawn on a flat map.
Modern aircrafts follow routes along sections of great circles for speedy long-distance flights and thus cut down flying time. But it is not always possible to follow great circle routes. Firstly, air routes must link numerous cities and thus planes proceed in short 'hops' from place to place; secondly, it may be impossible to fly along great circles for political reasons if some countries forbid the use of their air-space; thirdly, air routes tend to follow the land in case of accidend and rarely fly for long distances over the sea. However, where long distances have to be covered over uninhabited regions, great circle routes are the quickest. They are therefore used in crossing polar regions. Some of the major great circle routes over the pole include that from London to Vancouver or Los Angeles, that from Tokyo to Stockholm and that from Tokyo to Mexico City. Polar routes are not only quicker but also relieve air-traffic congestion on the very crowded conventional routes.

Wednesday, May 29, 2013

Day and Night (Earth's rotation)

When the earth rotates on its axis, only one portion of the earth's surface comes into the rays of the the sun and experiences daylight. The other portion which is away from the sun's rays will be in darkness. As the earth rotates from west to east, every part of the earth's surface will be brought under the sun at some time or other. A part of the earth's surface that emerges from darkness into the sun's rays experiences sunrise. Later, when it is gradually obscured from the sun's beams it experiences sunset. The sun is, in fact, stationary and it is earth which rotates. The illusion is exactly the same as when we travel in a fast-moving train. The trees and houses around us appear to move and we feel that the train is stationary.

Monday, May 27, 2013

Evidence of the Earth's Sphericity

There are many ways to prove that the earth is spherical. The following are some of them. 1. CIRCUMNAVIGATION OF THE EARTH. The first voyage around the world by Ferdinand Magellan and his crew, from 1519 to 1522, proved beyond doubt that the earth is spherical. No traveller going roumd the world by land or sea has eve encountered an abrupt edge, over which he would fall. Modern air routes and ocean navigation are based on the assumption that the earth is round. 2. THE CIRCULAR HORIZON. The distant horizon viewed from the deck of a ship at sea, or from a cliff on land is always and everywhere circular in shape. This circular horizon widens with increasing altitude and could only be seen on a spherical body. 3. SHIP'S VISIBILITY. When a ship appears over the distant horizon, the top of the mast is seen first before the hull. In the same way, when it leaves habour, its disappearance over the curved surface is equally gradual. If the earth were flat, the entire ship would be seen or obscured all at once. 4. SUNRISE AND SUNSET. The sun rises and sets at different times in different places. As the earth rotates from west to east, places in the east see the sun earlier than those in the west. If the earth were flat, the whole world would have sunrise and sunset at the same time. But we know this is not so. 5. THE LUNAR ECLIPSE. The shadow cast by the earth on the moon during a lunar eclipse is always circular. It takes the outline of an arc of a circle. Only a sphere can cast such a circular shadow. 6. PLANETARY BODIES ARE SPHERICAL. All observations from telescopes reveal that the planetary bodies, the sun, moon, satellites and stars have circular outlines from whichever angle you see them. They are strictly spheres. Earth, by analogy, cannot be the only exception. 7. DRIVING POLES ON LEVEL GROUND ON A CURVED EARTH. Engineers when driving poles of equal length at regular intervals on the ground have found they do not give a perfect horizontal level. The centre pole normally projects slightly above the poles at either end because of the curvature of the earth. Surveyors and field engineers therefore have to make certain corrections for this inevitable curvature, i.e. 12.6 cm to 1 km. 8. SPACE PHOTOGRAPHS. Pictures taken from high altitudes by rockets and satellites show clearly the curved edge of the earth. This is perhaps the most convincing and the most up-to-date proof of the earth's sphericity.

Sunday, May 26, 2013

The Shape of the Earth

In the olden days, sailors feared to venture far into the distant ocean because they thought that when they reached the edge of the earth, they would slip down and perish in the bottomless ocean. This is, of course, not true. From years of accumulated knowledge, experience and observations in different parts of the world, we know that the earth is round. Its spherical shape is an established fact, proved and accepted by all. There has been so much research done on earth science that its various dimensions have been accurately found. It has an equatorial circumference of 40,084 km and its polar circumference is less by 133 km. Its equatorial diameter is 12,761 km and its polar diameter is shorter by 42 km. This simply shows that the earth is not a perfect sphere. It is a little flattened at both ends like an orange. It can, in fact, be called a geoid ('earth-shaped'). The spherical shape of the earth is also masked by the intervening highlands and oceans on its surface.

The Solar System

The solar system comprises the sun and its nine planets which are believed to have been developed from the condensation of gases and other lesser bodies. All the planets revolve round the sun in elliptical orbits. Like the earth, they shine only by the reflected light of the sun. The sun has a surface temperature of 6000'C and increases to 20 million'C in the interior. All over its surface are fiery gases that leap up in whirls of glowing flames like a volcano in eruption. In size, the sun is almost unimaginable. It is about 300,000 times as big as the earth! Amongst the nine planets, MERCURY is the smallest and closest to the sun, only 57,900,000 km away. It thus completes its orbit in a much shorter space of time than does earth. A year in Mercury is only 88 days. VENUS, twice the distance away from the sun, is the next closest planet. It is often considered as "Earth's twin" because of their close proximity in size, mass (weight) and density. But no other planet is in any way comparable to EARTH which has life and all the living things we see around us. Like many other planets, the earth has a natural satellite, the moon, 384,629 km away, that revolves eastward around the Earth once in every 27 days. The fourth planet from the sun is MARS which has dark patches on its surface and is believed by most professional astronomers to be the next planet after Earth to have the possibility of some plant life. Much attention has been focused on Mars to explore the possibilities of extending man's influence to it. Next comes JUPITER, the largest planet in the solar system. Its surface is made up of many gases like hydrogen, helium and methane. It is distinguished from other planets by its circular light and dark bands, and the twelve satellites that circle round it. As it is more than 780 million km from the sun, its surface is very cold, probably about - 128'C. Another unique planet is SATURN which has three rings and nine satellites around it. In size, it is the second largest after Jupiter. It is so far from the sun that it takes 29 and half years to complete its orbit. The seventh planet, URANUS, was not known to astronomers until the late eighteenth century when it was first seen as a faint bluish-green disc through a very powerful telescope. It is another giant planet, 50 times larger than earth and 15 times as heavy. Unlike other planets, Uranus orbits around the sun in a clockwise direction from east to west with five satellites revolving round it. The two outermost planets in the solar system, Neptune and Pluto, are just visible with telescopes. Their discoveries were the result of mathematical calculations on their irregular gravitational effects on neighbouring planetary bodies. NEPTUNE closely resembles Uranus, except that it has only two known satellites and is probably much colder. Pluto is smaller than earth. As the orbits of the planets are not circular but elliptical, the distance of Pluto from the sun during perihelion (i.e. when it is closest to the sun) is 4451 million km, and at aphelion (i.e. when it is farthest from the sun) is 7348 million km. A year in PLUTO is no less than 247 years on earth! Due to their very recent discovery and their extreme remoteness from the earth, very little is so far known about these last two planets.

Exploring the Universe

On a bright night when you look up at the sky, it seems to be studded with stars. Little do you realize that each of the stars is far bigger than the earth on which we live. Some of the larger ones have been estimated to be many millions of times the size of the earth. The stars are not scattered regularly in space; they occur in clusters, better described as galaxies or nebulas. Each galaxy may contain as many as 100,000 million stars. The stars appear small to us even through a telescope because they are so far away. The light from the nearest star traveling at the speed of light (i.e. 299,400 kilometres/186,000 miles per second) takes something like four years to reach us. A ray of light from the sun takes about eight minutes to reach the earth. Light takes only a second to reach us from the moon. In recent years much interest has been shown and vast expenditure has been made, particularly by the United States and the Soviet Union, in exploring outer space. Many problems have had to be overcome. For example, the problem of meeting man's basic needs of oxygen, water and food; temperature control and the problem of weightlessness, while he is in outer space. A number of technological advances have been made in the course of these space programmes, particularly in the fields of radio and television communications. On 4 October 1957 the Soviet Union successfully launched the first artificial satellite (Sputnik I). This was followed by a series of unmanned spacecraft that sent back to earth television pictures of the surface features of the heavenly bodies, and coded information by radio. In April 1961 the Soviet Union successfully placed the first man, Yuri Gagarin, in orbit round the earth. Since then there have been many manned flights into outer space, culminating in the first landing on the moon by American astronauts in a rocket called Apollo 11 in July 1969. The importance of space exploration to man in general, and to geographers and other earth scientists in particular, is immense. Much has been learnt about space temperature, the magnetic fields of the sun and the earth, the amount and kinds of radiation, the shape and extent of the earth's upper atmosphere. We have learnt much about the surface of the moon and about human adaptability to its environment.